Hereditary Blindness in a Captive Wolf (Canis lupus) Population: Frequency Reduction of a Deleterious Allele in Relation to Gene Conservation

Numerous cases of hereditary diseases and disorders have been reported in wild animals bred in captivity, but little attention has been paid to the particular genetic management problems that arise when such defects occur. These problems include the obstacle of eliminating the deleterious allele(s) without contemporary loss of genetic variability. In this paper we use the statistical methods of pedigree analysis to address questions regarding a previously presumed hereditary form of blindness observed in a captive wolf population bred for conservation purposes in Scandinavian zoos. The most likely mode of inheritance coincides with an autosomal recessive allele with either a full penetrance or a reduced penetrance of 0.6 (depending on the reliability of studbook records). Using these two models of inheritance, we calculate the probability of carrying the blindness allele for each living animal. Analysis of the effect of removing high-probability carriers on founder allele survival and level of inbreeding demonstrates that the frequency of the deleterious allele can be significantly reduced without seriously affecting founder allele survival or current degree of inbreeding in the wolf population.     

No Inbreeding Depression Observed in Mexican and Red Wolf Captive Breeding Programs

Abstract: Inbreeding depression is expected to affect populations of outbreeding mammals in inverse proportion to their population size and can affect whether small populations persist or go extinct. We used studbook records to examine the effect of inbreeding upon juvenile viability and litter size in two endangered species that have recently been reintroduced to the wild: the Mexican wolf ( Canis lupus baileyi ) and the red wolf ( C. rufus ). We found that neither juvenile viability nor litter size was lowered by inbreeding in either taxon. In fact, both captive breeding programs appear to have less lethal equivalents than the median estimate for mammals. We did find that year of birth was correlated with increasing viability in both taxa. We conclude that there is no evidence that inbreeding depression will prove a major obstacle to the success of either recovery effort.     

Inbreeding Depression in the Speke's Gazelle Captive Breeding Program

Abstract: The Speke's gazelle ( Gazella spekei ) captive breeding program has been presented as one of the few examples of selection reducing the genetic load of a population and as a potential model for the captive breeding of endangered species founded from a small number of individuals. In this breeding program, three generations of mate selection apparently increased the viability of inbred individuals. We reanalyzed the Speke's gazelle studbook and examined potential causes for the reduction of inbreeding depression. Our analysis indicates that the decrease in inbreeding depression is not consistent with any model of genetic improvement in the herd. Instead, we found that the effect of inbreeding decreased from severe to moderate during the first generation of inbreeding, and that this change is responsible for almost all of the decline in inbreeding depression observed during the breeding program. This eliminates selection as a potential explanation for the decrease in inbreeding depression and suggests that inbreeding depression may be more sensitive to environmental influences than is usually thought.     

Inbreeding Depression, Environmental Stress, and Population Size Variation in Scarlet Gilia (Ipomopsis aggregata)

Despite a large body of theory, few studies have directly assessed the effects of variation in population size on fitness components in natural populations of plants. We conducted studies on 10 populations of scarlet gilia, Ipomopsis aggregata , to assess the effects of population size and year-to-year variation in size on the relative fitness of plants. We showed that seed size and germination success are significantly reduced in small populations (those 100 flowering plants) of scarlet gilia. Plants from small populations are also more susceptible to environmental stress. When plants from small and large populations were subjected to an imposed stress (combined effects of transplanting and experimental clipping, simulating ungulate herbivory) in a common garden experiment, plants from small populations suffered higher mortality and were ultimately of smaller size than plants from large populations. In addition, experimental evidence indicates that observed fitness reductions are genetic, due to the effects of genetic drift and/or inbreeding depression. When pollen was introduced from distant populations into two small populations, seed mass and percentage of germination were bolstered, while pollen transferred into a large population had no significant effect. Year-to-year variation in population size and its effects on plant fitness are also discussed. In one small population, for example, a substantial increase in size from within did not introduce sufficient new (archived) genetic material to fully overcome the effects of inbreeding depression.     

Inbreeding and Outbreeding Depression in Natural Populations of Chamaecrista fasciculata (Fabaceae)

Abstract: The deleterious consequences of inbreeding have been well documented. There are, however, few empirical studies that have examined the consequences of restoring heterozygosity and hence the fitness of inbred populations by conducting interpopulation crosses and measuring the performance of later-generation hybrids under field conditions. We conducted interpopulation crosses of 100 m to 2000 km, which spans the range of Chamaecrista fasciculata ( Fabaceae) in eastern North America. We then contrasted the performance of the F1 and later-segregating F3 hybrids with the parental generation. We found almost universal F1 superiority over the parents. The F3 hybrids suffered a loss of fitness compared to the F1 hybrids. The drop off in fitness of the F3 reflects both the loss of heterozygosity and the disruption of coadapted gene complexes. The F3 performance, however, was still often equal to that of the parents, suggesting that heterosis can outweigh the loss of coadaptation except for the longest-distance crosses. In a subset of environments, the F3 performance of long-distance (≥1000 km) interpopulation crosses was less than that of both parents and indicated true outbreeding depression. For C. fasciculata , it appears that crossing populations of up to intermediate distances of hundreds of kilometers has a short-term beneficial effect on progeny performance through F1, and that longer-term effects are not necessarily disruptive of fitness, at least relative to parental performance. The degree of F1 heterosis and F3 outbreeding depression varied between site and year, however, indicating an important role for the environment in the expression of these effects.     

Unprecedented Low Levels of Genetic Variation and Inbreeding Depression in an Island Population of the Black-Footed Rock-Wallaby

Abstract: It has been argued that demographic and environmental factors will cause small, isolated populations to become extinct before genetic factors have a significant negative impact. Islands provide an ideal opportunity to test this hypothesis because they often support small, isolated populations that are highly vulnerable to extinction. To assess the potential negative impact of isolation and small population size, we compared levels of genetic variation and fitness in island and mainland populations of the black-footed rock-wallaby ( Petrogale lateralis [Marsupialia: Macropodidae]). Our results indicate that the Barrow Island population of P. lateralis has unprecedented low levels of genetic variation (  H _e = 0.053, from 10 microsatellite loci) and suffers from inbreeding depression (reduced female fecundity, skewed sex ratio, increased levels of fluctuating asymmetry). Despite a long period of isolation ( ∼ 1600 generations) and small effective population size (  N _e ∼ 15), demographic and environmental factors have not yet driven this population to extinction. Nevertheless, it has been affected significantly by genetic factors. It has lost most of its genetic variation and become highly inbred (  F _e = 0.91), and it exhibits reduced fitness. Because several other island populations of P. lateralis also exhibit exceptionally low levels of genetic variation, this phenomenon may be widespread. Inbreeding in these populations is at a level associated with high rates of extinction in populations of domestic and laboratory species. Genetic factors cannot then be excluded as contributing to the extinction proneness of small, isolated populations.     

Inbreeding avoidance in a poeciliid fish (Heterandria formosa)

Polyandry is hypothesized to give females an opportunity to avoid inbreeding through postcopulatory selection mechanisms if precopulatory inbreeding avoidance is not possible, for example, because of forced matings. Here, we report a postcopulatory, prefertilization, inbreeding avoidance mechanism in the least killifish, Heterandria formosa, a species in which males can force matings. Females had 50% less sperm in their oviducts and ovarian cavities after mating with a sibling compared to a mating with a nonsibling male. Neither sex showed inbreeding avoidance in a dichotomous precopulatory mate choice test or during mating trials. Females in this species invest substantially in each offspring after fertilization (matrotrophy), whereas males invest little more than sperm. Based on theory, females should therefore be more likely than males to avoid inbreeding in this species. We suggest that females do this by reducing the amount of sibling sperm in their reproductive system. However, the possibility that males invested more sperm to nonsiblings could not be ruled out. In a fertilization success experiment, the first male to mate with a female sired all the offspring in most cases, even if it was a sibling. However, large females were more likely to carry offspring of multiple males. Possibly female sperm storage sites were filled by the first male, and only large females had space for the second male's sperm.     

中国动物园圈养丹顶鹤的数量和分布格局

通过电话咨询、实地调查和网络检索的方法调查了141个城市动物园、园中园和野生动物园的丹顶鹤圈养情况,以明确我国动物园圈养丹顶鹤的种群数量和分布格局。结果表明,141个动物园中,83个(58.9%)动物园有数量不等的圈养丹顶鹤(1~175只),总数达到917只;其中城市动物园319只,园中园82只,野生动物园516只。不同地区的不同动物园圈养丹顶鹤分布有明显差异。单因素方差分析表明野生动物园丹顶鹤数量显著大于园中园(P0.05)。圈养丹顶鹤最多的3个省级行政区分别为辽宁省、广东省和黑龙江省;圈养丹顶鹤数量最多的前10个省级行政区共圈养丹顶鹤719只,占中国动物园圈养丹顶鹤总数的78.4%。圈养丹顶鹤最多的3个地理区域分别为东北地区、华东地区和华北地区,占我国动物园圈养丹顶鹤总数的74.3%。     

Estimates of Natural Selection in a Salmon Population in Captive and Natural Environments

Abstract:  Captive breeding is a commonly used strategy for species conservation. One risk of captive breeding is domestication selection—selection for traits that are advantageous in captivity but deleterious in the wild. Domestication selection is of particular concern for species that are bred in captivity for many generations and that have a high potential to interbreed with wild populations. Domestication is understood conceptually at a broad level, but relatively little is known about how natural selection differs empirically between wild and captive environments. We used genetic parentage analysis to measure natural selection on time of migration, weight, and morphology for a coho salmon ( Oncorhynchus kisutch ) population that was subdivided into captive and natural components. Our goal was to determine whether natural selection acting on the traits we measured differed significantly between the captive and natural environments. For males, larger individuals were favored in both the captive and natural environments in all years of the study, indicating that selection on these traits in captivity was similar to that in the wild. For females, selection on weight was significantly stronger in the natural environment than in the captive environment in 1 year and similar in the 2 environments in 2 other years. In both environments, there was evidence of selection for later time of return for both males and females. Selection on measured traits other than weight and run timing was relatively weak. Our results are a concrete example of how estimates of natural selection during captivity can be used to evaluate this common risk of captive breeding programs.     

Inbreeding and Loss of Genetic Variation in a Reintroduced Population of Mauritius Kestrel

Abstract:  Many populations have recovered from severe bottlenecks either naturally or through intensive conservation management. In the past, however, few conservation programs have monitored the genetic health of recovering populations. We conducted a conservation genetic assessment of a small, reintroduced population of Mauritius Kestrel ( Falco punctatus ) to determine whether genetic deterioration has occurred since its reintroduction. We used pedigree analysis that partially accounted for individuals of unknown origin to document that (1) inbreeding occurred frequently (2.6% increase per generation; N _eI= 18.9), (2) 25% of breeding pairs were composed of either closely or moderately related individuals, (3) genetic diversity has been lost from the population (1.6% loss per generation; N _eV= 32.1) less rapidly than the corresponding increase in inbreeding, and (4) ignoring the contribution of unknown individuals to a pedigree will bias the metrics derived from that pedigree, ultimately obscuring the prevailing genetic dynamics. The rates of inbreeding and loss of genetic variation in the subpopulation of Mauritius Kestrel we examined were extreme and among the highest yet documented in a wild vertebrate population. Thus, genetic deterioration may affect this population's long-term viability. Remedial conservation strategies are needed to reduce the impact of inbreeding and loss of genetic variation in this species. We suggest that schemes to monitor genetic variation after reintroduction should be an integral component of endangered species recovery programs.     

Stress Resistance and Environmental Dependency of Inbreeding Depression in Drosophila melanogaster

Abstract: Both inbreeding and environmental stress can have adverse effects on fitness that affect the conservation of endangered species. Two important issues are whether stress and inbreeding effects are independent as opposed to synergistic, and whether inbreeding effects are general across stresses as opposed to stress-specific. We found that inbreeding reduced resistance to acetone and desiccation in adult Drosophila melanogaster , whereas resistance to knockdown heat stress was not affected. Inbred flies, however, experienced a greater proportional decrease in productivity than outbreds following heat stress. Correlations using line means indicated that all resistance traits were uncorrelated in the inbred as well as in the outbred flies. Recessive, deleterious alleles therefore did not appear to have any general deleterious effects on stress resistance. Inbreeding within a specific environment and selection for resistant genotypes may therefore purge a population of deleterious genes specific to only one environmental stress.     

Long-Term Population Development of a Reintroduced Beaver (Castor fiber) Population in Sweden

Deliberate reintroductions of locally exterminated animal species to areas within their former ranges is an increasingly important conservation tool. Most reintroductions are fairly recent and still in an initial phase of population development. There are few long-term studies of reintroduced populations. The aim of this study was to see if the population development of the reintroduced European beaver ( Castor fiber ) population in Sweden exhibits the same pattern of population development as other introductions, in accordance with general theories, and to discuss possible management consequences. Since the European beaver was reintroduced to Sweden 70 years ago, the population has developed in a way predicted by the Riney-Caughley model for introduced ungulates, exhibiting an irruption and a subsequent decline. In two study areas, the rate of population increase (r) turned negative after 34 and 25 years and at densities of 0.25 and 0.20 colonies/km², respectively. The data suggest that management policy for an irruptive species should allow hunting during the rapid-increase phase, thus maintaining food resources and avoiding uncontrolled population decline.     

Linking Inbreeding Effects in Captive Populations with Fitness in the Wild: Release of Replicated Drosophila melanogaster Lines under Different Temperatures

Abstract:  Inbreeding effects have been detected in captive populations of threatened species, but the extent to which these effects translate into fitness under field conditions is mostly unknown. We address this issue by comparing the performance of replicated noninbred and inbred Drosophila lines under field and laboratory conditions. We asked whether environment-dependent effects of inbreeding can be demonstrated for a field-fitness component in Drosophila , the ability of flies to locate resources, and associated the results with results on effects of inbreeding investigated in the laboratory. Inbreeding effects were evident when releases were undertaken under warm conditions, but not under cold conditions, which illustrates the environment-dependent nature of inbreeding depression. Inbreeding effects were much stronger in the field at warm temperatures than in laboratory stress tests, particularly for females. Effects of inbreeding based on performance in traditional inbreeding assays (viability, productivity) or from laboratory stress tests poorly predicted performance in the field. Inbreeding effects on resource location in the field can be strongly deleterious under some thermal conditions and involve traits not easily measured under laboratory conditions. More generally, inbreeding effects measured in captive populations may not necessarily predict their field performance, and programs to purge captive populations of deleterious alleles may not necessarily lead to fitness benefits in the wild.     

Quantitative and Molecular Genetic Variation in Captive Cotton-Top Tamarins (Saguinus oedipus)

Most genetic surveys of captive and endangered populations are carried out with single gene characters bearing no direct relationship to life history or other features for which genetic variation needs to be maintained. Quantitative genetic estimates of heritable variation for life-history traits may be a more direct and appropriate measure of genetic variation for some conservation purposes. Furthermore, recent theoretical and empirical results indicate that genetic variation measured on these two levels may not be concordant. We analyzed heterozygosity at 41 allozyme loci and heritability for body weight in captive cotton-top tamarins ( Saguinus oedipus ) from the Marmoset Research Center of the Oak Ridge Associated Universities in order to compare these two levels of genetic variation. Cotton-top tamarins are a highly endangered species native to Colombia. Many animals currently reside in research facilities and zoological parks. A total of 106 animals were used in the isozyme survey, while data on 364 animals contributed to the quantitative genetic study of body weight. We found a very low average heterozygosity ( H = 1%) for this colony. Body weight was moderately and significantly heritable ( h ² = 35%). This heritability is within the normal range for natural animal populations. The finding of biologically significant levels of heritability in a population with abnormally low allozyme heterozygosity illustrates the point that low levels of allozyme heterozygosity should not be taken as an indication of overall lack of genetic variation in important quantitative characters such as life-history traits. Genetic variation required for adaptation of species to future environmental challenges can exist despite low levels of enzyme heterozygosity.     

Male philopatry,extra-pack copulations and inbreeding avoidance in Ethiopian wolves (Canis simensis)

Monogamous pairings have been regarded as the fundamental social unit in all canid species, including those living in packs. In Ethiopian wolves, however, habitat saturation limits dispersal, which raises the question of whether they avoid inbreeding and, if so, by what mechanism. In two study areas Ethiopian wolf packs had stable memberships. Each pack comprised two to eight adult males, one to three adult females, including a clear-cut dominant individual of each sex, together with one to six yearlings and up to six pups (n = 9 packs). Males remained in their natal packs, apparently throughout their lives. Some females also failed to disperse while others dispersed in their second or third year and became floaters. Dominant females monopolized breeding, and were succeeded either by their most dominant daughters (three cases) or by floaters (two cases). In the former case there is potential for incest; however, 70% of 30 copulations observed were between the dominant female of one pack and a male from an adjoining pack. In Ethiopian wolves, under conditions where dispersal is constrained and the potential for inbreeding is high, extra-pack matings (and associated multiple paternity) result in outbreeding. We raise the possibility that extra-pair copulations may be widespread in canid societies and that the monogamy supposedly fundamental to the family may be more sociological than genetic. Received: 15 October 1994/Accepted after revision: 9 December 1995     

Relative Contribution of Inbreeding Depression and Eroded Adaptive Diversity to Extinction Risk in Small Populations of Shore Campion

Abstract:  To study the relative importance of inbreeding depression and the loss of adaptive diversity in determining the extinction risk of small populations, we carried out an experiment in which we crossed and self-fertilized founder plants from a single, large population of shore campion ( Silene littorea Brot.). We used the seeds these plants produced to colonize 18 new locations within the distribution area of the species. The reintroduced populations were of three kinds: inbred and genetically homogeneous, each made up of selfed seed from a single plant; inbred and mixed, made up of a mixture of selfed seeds from all founder plants; and outbred and mixed, made up of a mixture of seeds obtained in outcrosses between the founders. We compared the inbred homogeneous populations with the inbred mixed to measure the effect of genetic diversity among individuals and the inbred mixed with the outbred mixed to measure the effect of inbreeding. Reintroduction success was seriously limited by inbreeding, whereas it was not affected by genetic diversity. This observation and the nonsignificant interaction between family and reintroduction location for individual plant characters suggest that the fixation of overall deleterious genes causing inbreeding depression posed a more serious threat to the short-term survival of the populations than the loss of genes involved in genotype and environment interactions. Thus, reintroduction success was related to adaptive diversity. Preventing such fixation might be the most important consideration in the genetic management and conservation of shore campion populations.     

The Effects of Selective Logging on Inbreeding in Shorea megistophylla (Dipterocarpaceae) from Sri Lanka

The mating system of Shorea megistophylla , an endemic canopy tree from Sri Lanka, was quantified by allozyme analysis of progeny arrays using a mixed-mating model. Two adjacent populations were compared: one in forest that was selectively logged about 20 years ago, and the other in undisturbed primary forest. The selectively logged population had a lower multilocus outcrossing rate (t_m, = 0.71) compared to that of the undisturbed forest (t_m = 0.87). Only the progeny from the logged population showed evidence of either biparental inbreeding or Wablund effect, and the genotypic frequencies violated the assumptions of the mixed-mating model. Apomixis was detected in one isolated tree in the Royal Botanical Garden in Peradeniya by a multilocus test of progeny genotypic frequencies relative to the maternal genotype. However, significant levels of apomixis were not discerned in the natural (logged and unlogged) populations. These findings indicate that a reduction in population density of S. megistophylla following selective logging can significantly elevate the proportion of seeds produced through inbreeding. Adventive embryony may also increase in isolated trees that lack the chance to outcross.     

Inbreeding in a lek-mating ant species, Pogonomyrmex occidentalis

In this paper we have two goals. First, we examine the effects of sample size on the statistical power to detect a given amount of inbreeding in social insect populations. The statistical power to detect a given level of inbreeding is largely a function of the number of colonies sampled. We explore two sampling schemes, one in which a single individual per colony is sampled for different sample sizes and a second sampling scheme in which constant sampling effort is maintained (the product of the number of colonies and the number of workers per colony is constant). We find that adding additional workers to a sample from a colony makes it easier to detect inbreeding in samples from given number of colonies; however, adding more colonies rather than more workers per colony always gives greater power to detect inbreeding. Because even relatively large amounts of sib-mating generate relatively small inbreeding coefficients, detection of even substantial deviations from random mating will require very large samples. Second, we look at the amount of inbreeding in a large population of the western harvest ant, Pogonomyrmex occidentalis. We find deviations from Hardy-Weinberg equilibrium equivalent to approximately 27% sib-mating in our population ( f = 0.09). Review of past studies on the population structure of other Pogonomyrmex species suggests that inbreeding may be a regular feature of the mating system of these ants. Although P. occidentalisis a swarm-mating species, there are a number of features of its population biology which suggest that the effective population size may be small. These include topographical variation that potentially breaks the population into demes, variation in the reproductive output of colonies, and variation in the size of reproductives produced by colonies. Received: 6 May 1996 / Accepted after revision: 6 October 1996